• Composites Research
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• v.24 no.2
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• pp.46-50
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• 2011

This paper describes the state of the art for the development of metallic armor materials which are mainly used as armor plates of the combat vehicles. Several important micro-structural features affecting ballistic properties of the metallic armor are discussed. Optimization of the strength and toughness balance of the metallic armor is necessary for the improvement of the ballistic performance resulting from maximizing the resistance to the penetration of the bullet and also to brittle failure of the plates. Understanding and control of the adiabatic shearing phenomenon developed remarkably during high strain rate deformation is needed to prevent brittle failure of the metallic armor materials.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.43-44
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• 2006

Generally almost all fatigue crack growth is affected by model. For this reason a study on model has concentrated in the field of fracture mechanics. However the fatigue crack initiation and growth in machines and structures usually occur in mixed mode loading. If there is any relationship between the cause of fracture in mixed mode loading and fracture surface, fracture surface pattern will be the main mean explaining reasons of fatigue fracture and obtaining further information about fracture process. In this paper four point shear-fatigue test with Aluminum alloy Al 5083-O is carried out from this prospect and then the mixed mode distribution of fracture surface is examined from the result after identifying the generation of fatigue crack surface pattern. It was found from the experimental results that the fatigue crack surface pattern and the fatigue crack shear direction are remarkably consistent. Furthermore It is possible that the analysis of distribution of mixed mode through the fatigue crack surface pattern.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1157-1162
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• 2003

Behavior of aluminum alloy embedding a particle was investigated at room temperature under ECAP. Finite element analysis by using ABAQUS shows that ECAP is a useful tool for eliminating residual porosity in the specimen, and much more effective under friction condition. The simulation, however, shows considerably low density distributions for matrix near a particle at which rich defects may occur during severe deformation. Finite element results of effective strains and deformed shapes for matrix with a particle were compared with theoretical calculations under simple shear stress. Also, based on the distribution of the maximum principal stress in the specimen, Weibull fracture probability was obtained for particle sizes and particle-coating layer materials. The probability was useful to predict the trend of more susceptible failure of a brittle coating layer than a particle without an interphase in metal matrix composites.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.43.2-43.2
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• 2018

송전 및 배전선 선로에 사용되는 핵심 부품인 ACSR (Aluminum Conductor Steel Reinforced, 강심 알루미늄 연선) cable은 우수한 기계적 성질, 가벼운 중량, 내부식성 특징을 가지고 있어 송전 및 배전선 선로에 핵심 부품으로 사용된다. 하지만, 국내외 혹한 다설 지역에 설치된 ACSR cable에서 빙설해로 인한 단락 또는 지락 사고가 지속적으로 발생하고 있다. 빙설해에 의한 송전선로의 고장은 급격한 전압 강하로 인해 전기 품질에 큰 영향을 주어 민원제기의 주요 원인이 되며, 고장의 파급효과가 국지적으로 발생하지 않고 광범위하게 발생하는 특징이 있기 때문에 이에 대한 대응이 필요한 실정이다. 이러한 문제를 해결하기 위해 ACSR cable의 주 소재인 알루미늄에 대한 판상(Plate) 결빙강도 파악 및 결빙방지 소재개발 연구가 국내외에서 활발히 진행 중이나, 실제 원형의 전선다발이 나선형으로 감겨있는 구조의 ACSR cable 결빙 접합강도를 시험을 통해서 명확히 제시한 연구결과는 아직 보고된 바 없다. 본 연구에서는 실제 송전용 ACSR cable을 대상으로 얼음 간의 주 전단 응력, 파단에너지 등의 결빙특성을 정량적으로 측정할 수 있는 3D 스캔을 활용한 결빙특성 평가시험기를 개발하고, 345kV급 ACSR cable에 대한 결빙특성을 평가결과를 제시하였다. 또한 ACSR cable에 현재 상용화되고 있는 결빙방지 코팅소재를 적용함으로써 코팅소재의 적합성을 ARF(Adhesion reduction factor) 지표를 통해서 비교 평가한 결과를 포함한다.

• Elastomers and Composites
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• v.36 no.2
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• pp.86-93
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• 2001

For solving the environmental problem of the waste EPDM and for new TPE blend materials, we developed a new kind of TPE material using a co-rotating twin screw extruder. To improve the mechanical properties of TPE material such as tensile strength, elongation at break, and modulus of the blend, PP and waste EPDM powder were blended with different screw configurations. The mechanical properties of the blends and morphology of the TPE were investigated. As the number of kneading disc and left-handed screw element increased, dynamic vulcanization of the material was increased because the shear stress and residence time of blends increased.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.2
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• pp.157-167
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• 2008

Six smooth flat tensile specimens and eighteen punch specimens with three different thicknesses were machined from steel of JIS G3131 SPHC. In addition to punch tests, incremental tensile tests were conducted to obtain average true flow stress - logarithmic true strain curves. Through parametric FE simulations for the tensile specimens, material parameters related to GTN model were identified. Using indenters with three kinds of radius, punch tests were carried out to obtain fracture characteristics of punch specimens. Numerical analyses using both fracture models, GTN and $J_2$ plasticity model, gave that the former estimated well the fracture of punch specimen but the latter did not. A new concept for critical size of plate elements was introduced based on minimum relative sharpness between contact structures. Consequently, a new criterion for critical element size was proposed to be less than 20% of minimum relative radius of interacting structures.

• Transactions of Materials Processing
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• v.32 no.2
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• pp.92-99
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• 2023

In this study, shear fracture specimens are designed using finite element analyses for the characterization of ductile fracture criteria of metal sheets. Many recently suggested ductile fracture criteria require experimental fracture data at the shear stress states in the model parameter identification. However, it is challenging to maintain shear stress states in tension-based specimens from the initial yield to the final fracture, and the loading path can be different for the different materials even with the same shear specimen geometries. To account for this issue, two different shear fracture specimens for low ductility/high ductility metal sheets are designed using the sensitivity tests conducted by finite element simulations. Priorly mechanical properties including the Hosford-Coulomb fracture criterion of the aluminum alloy 7075-T6 and DP590 steel sheets are used in the simulations. The results show that shear stress states are well-maintained until the fracture at the fracture initiation points by optimizing the notch geometries of the shear fracture specimens.

• Composites Research
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• v.29 no.2
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• pp.79-84
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• 2016

An adhesive can be used to connect two different materials in structures. In comparing with other connecting methods, such as bolt, rivet, and hot melting, the adhesive does not need to use them. It leads to reduce the weight and decrease the stress concentration along the connecting line. This work studied the comparison of mechanical and interfacial properties of commonly-used two adhesives, acrylic type and bisphenol-A epoxy type. Tensile and flexural strength of neat adhesives were also compared. Lap shear test of two adhesives was deduced from the measurement of tensile and fatigue tests. After testing, the failure patterns of adhesive surfaces were observed by a microscope. Tensile strength and mechanical fatigue resistance at using bisphenol-A epoxy adhesive were better than acrylic adhesive. Also adding CNT reinforcement in epoxy adhesive can anticipate mechanical improvement.

• Journal of Adhesion and Interface
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• v.16 no.2
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• pp.69-75
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• 2015

Stone board for the rock bed was needed to reduce weight using thin thickness and reinforced materials. In this work, stone/wood board for rock bed was studied. Stone and wood were attached to reduce total weight of stone for rock bed. For reinforcing wood heat treatment method was used to change surface and mechanical properties. Mechanical strength of heat treated wood increased more than neat condition. The optimum heat treatment condition was set on $100^{\circ}C$ under tensile, flexural loads whereas surface energy was also obtained by contact angle measurement. Optimum adhesive condition was to get the maximum adhesion between stone and wood. Lap shear test was performed for stone/wood board with different adhesives such as amine type epoxy, polyurethane, chloro-rubber and vinyl chloride acetate type. Fracture surface of lap shear test was shown at wood fracture part on stone using amine type epoxy adhesive. It was found that for high adhesion between stone and wood the optimum adhesive was epoxy type for the rock bed.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.1
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• pp.1-6
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• 2014

Flip chip bonded LED packages possess lower thermal resistance than wire bonded LED packages because of short thermal path. In this study, thermal and bonding properties of flip chip bonded high brightness LED were evaluated for Au-Sn thermo-compression bonded LEDs and Sn-Ag-Cu reflow bonded LEDs. For the Au-Sn thermo-compression bonding, bonding pressure and bonding temperature were 50 N and 300oC, respectively. For the SAC solder reflow bonding, peak temperature was $255^{\circ}C$ for 30 sec. The shear strength of the Au-Sn thermo-compression joint was $3508.5gf/mm^2$ and that of the SAC reflow joint was 5798.5 gf/mm. After the shear test, the fracture occurred at the isolation layer in the LED chip for both Au-Sn and SAC joints. Thermal resistance of Au-Sn sample was lower than that of SAC bonded sample due to the void formation in the SAC solder.